Aircraft on-board control systems typically require a ‘weight on wheels’ or ‘weight off wheels’ signal (each of which will be referred to as a ‘WoW’ signal) to be detected before allowing an operator to perform certain landing-specific functions, such as deploying lift dumping devices and applying landing gear brakes.
It is known to use mechanical closure of the main shock absorbing strut to provide a WoW signal; for example, a sensor such as a proximity sensor can be switched on when a main shock absorbing strut attains a predetermined state of compression. Such sensors will be referred to herein as compression-based WoW sensors.
The design of aircraft landing gear shock absorbers is often a compromise between shock absorber simplicity and the need to balance the weight, stroke, internal pressure, and the initial ‘breakout’ force required to start the shock absorber compressing.
Shock absorber breakout force can be described as the sum of the gas pressure multiplied by the effective area of the shock absorber in addition to any friction effects in the shock absorber system. Increasing the effective area of a shock absorber or increasing its inflation pressure has the effect of directly increasing its breakout force. While the breakout force does not adversely affect normal operation of the shock absorber, it can adversely affect the shock absorber's ability to close rapidly during light landings, where the aircraft landing force acting on the shock absorber is below average.
The present inventor has identified that known aircraft landing gear assembly compression-based WoW sensors can be made more reliable, simplified in design and/or reduced in size and/or weight.